1. Field of the Invention
The invention relates to an abrasive article comprising abrasive grain, e.g. corundum, a binder agent such as a binder material, e.g. phenolic resin, or a sintered magnesite bond and active fillers or fillers.
2. Description of the Prior Art
As already mentioned, abrasive disks, e.g. used for severing, comprise three essential components, i.e. the abrasive grain, a binder material or agent for holding the abrasive grain and active fillers.
The present invention relates to the problem of active fillers.
In the grinding operation, such active fillers effect chemical and physical processes which have a positive influence on the behaviour of the abrasive. Such fillers should in particular cause an increase in the service life of the abrasive tool and a decrease heating of the workpiece and the abrasive article and, hence, avoid thermal destruction. In some materials which are hard to cut, e.g. unalloyed, low carbon steels or titanium, such fillers are the prerequisite for economic processing.
Their effects are commonly categorized into the following three major groups:
1. Decrease in the friction between abrasive grain, workpiece and chips, i.e. the fillers and their by-products must have the effect of high temperature lubricants or high pressure lubricants. They can thereby form a primary lubricating film of melted mass (e.g. cryolite) or a solid lubricating film (graphite, molybdenum sulfide, lead oxide). Secondary films may also be formed: metallic chloride (-sulfide) as a filter.fwdarw.chlorine- (sulfur-) -separation.fwdarw.metallic chloride (-sulfide) of the ground material.
2. Protective effect by forming primary or secondary surface films on the abrasive grain, workpiece and chips (analogous to item 1). Grain destruction due to diffusion processes (e.g. spinel formation when grinding iron material containing corundum), welding of the grit to the grain or to the workpiece are thereby avoided.
3. Cooling effects in the microrange due to high melting-, vaporization- and phase change temperatures and thermal phase change points favourable in respect of temperature.
Numerous substances can, however, not or only under certain circumstances be employed in practice as they are expensive (noble metal halegonides, molybdenum sulfide), toxic (arsenic-, selenium-, lead compound), reduce the disk stability (e.g. graphite, sulfur), are of hygroscopic or high water solubility (numerous chlorides) and strongly react with the uncured phenolic resin system (hygroscopic chlorides).
Summing up, it may be said that an optimal active filler must have favourable phase change temperatures and chemically reactive separation products. The filler and its by-products should have a toxicity as low as possible and, hence, high threshold limit values, it should further be inexpensive and its being processed in abrasive articles should be commercially possible, i.e. not only under laboratory conditions.
Particularly the manufacture of disks using resol as the binder material has the disadvantage that the binder material binds prematurely.